A major fish kill occurred at Lake Fairfield August 25 through 26, according to Texas Parks and Wildlife Department (TPWD) Inland Fisheries biologist Richard Ott.
Fish kills also occurred on Lake Fairfield in 2008 and 2009, but this year’s kill was several weeks earlier and of much greater magnitude.
An estimated 1,255,674 fish were killed, which was higher than previous years (914,189 in 2009 and 121,568 in 2008). The majority of the fish by number were threadfin shad, gizzard shad, and tilapia but also included sunfishes and common carp. However, a substantial number of game fishes were also killed in this event, including an estimated 27,731 red drum; 48,176 largemouth bass; 1,474 channel catfish and 313 flathead catfish.
Luminant Power staff noticed dead fish the morning of August 25 and notified TPWD Inland Fisheries management and Kills and Spills Team (KAST) biologists. TPWD personnel arrived at the scene that afternoon and began assessing the situation to determine the extent of the kill.
Dead fish were located along 12.25 miles of shoreline from the dam to the effluent cove on the west side of the reservoir and to Big Brown Creek cove on the east shoreline. Dead fish were also abundant on the surface throughout the lower half of the reservoir.
Water quality datasondes (electronic data-gathering devices) were deployed in the northwest cove (within the kill zone) and offshore of the south boat ramp (outside the kill zone) to provide water temperature and dissolved oxygen data at 30-minute intervals over a several-week period. Six detailed shoreline counts and eight open-water transects of dead fish were conducted in randomly selected sections to allow estimation of the total kill.
Water quality data collected at Lake Fairfield on August 25 indicated extensive areas of lower-than-normal dissolved oxygen in the areas where the fish kill occurred. Dissolved oxygen levels below 5 mg/L cause stress and levels below 3 mg/L are fatal to most species of fish.
Daytime dissolved oxygen levels of 0-3 mg/L were recorded August 25 and dropped to 0 mg/L that night. Datasondes documented additional low-oxygen events from August 31- September 2 and again from September 4 to 8, but no additional fish kills have been reported.
The numbers of red drum and largemouth bass killed were considerably above the 2009 fish kill estimates of 1,579 red drum and 1,928 largemouth bass and 2008 estimates of 3,718 red drum and 257 largemouth bass. To put these numbers in perspective, anglers only harvested an estimated 1,329 red drum and 211 largemouth bass during the September 2008 through May 2009 creel survey. TPWD has stocked over 6.2 million red drum in Fairfield since 1984, and anglers spent over 9,000 hours seeking them at Lake Fairfield during the six-month creel survey in 2008-2009.
Normally microscopic plants called phytoplankton produce oxygen using a process called photosynthesis during daylight hours and increase oxygen concentration enough to compensate for respiration (oxygen use) by those same phytoplankton and fish as well as bacterial decomposition. However, during periods of cloudy weather, sunlight (measured as solar radiation) is reduced; oxygen consumption remains high but oxygen production is greatly reduced. When cloudy weather lasts for several days and oxygen concentration falls below the minimum level to support aquatic life, fish begin to die.
Because the watershed for Lake Fairfield is small relative to lake volume, make-up water is pumped from the Trinity River to maintain elevation. Trinity River water is high in nutrients, which are further concentrated in Lake Fairfield due to evaporation and lack of water discharge through the dam. This high level of nutrients contributes to high phytoplankton and fish production in Lake Fairfield but also contributes to dissolved oxygen depletion during cloudy weather.
TPWD biologists began to unravel the ecological factors contributing to fish kills on Lake Fairfield in fall 2009. By combining oxygen data from the datasondes with solar radiation data from a local weather station, biologists were able to understand the mechanisms leading to repeated kills at Lake Fairfield.
In late August and September, water temperature and bacterial activity are still high but day length shortens incrementally. In power-plant reservoirs such as Fairfield, water temperature and day length can become out of phase and increase the probability of fish kills.
Similar fish kills have also been reported at other power-plant lakes such as Victor Braunig and Calaveras near San Antonio but are of much lower magnitude than those at Lake Fairfield.
“It is unknown how the present fish kill will affect the fishery at Lake Fairfield,” Ott said. “TPWD staff will conduct additional fish sampling at Lake Fairfield this fall and next spring. Staff will be able to compare catch rates and size distribution to sampling in fall 2008 and spring 2009 and will be better able to assess the population effects to each species.”
Additional information about the kill and comparative size distribution of fishes involved over the past three years is available on the Inland Fisheries District 3-C Facebook page at www.facebook.com/TPWDIFTyler
The TPWD Kills and Spills Team is a group of biologists who respond to pollution reports or natural incidents that threaten state fish or wildlife resources. If you see dead or dying fish or wildlife or pollution threatening fish and wildlife, please contact the 24-hour Communication Center at (512) 389-4848, or contact your local game warden.
Additional information about KAST is available at http://archive.tpwd.state.tx.us/landwater/water/environconcerns/kills_and_spills/index.phtml.
Questions about the Lake Fairfield fishery should be directed to District Biologist Richard Ott at (903)-566-2161, email@example.com